What is the process to file for a litigation of disputed property?

I have booked flat in Pune sanaswadi location in Mapple group society. In December 2014 and as per agreement our possession date was (period 30months), as per date possession date was June 2017 but till date I not got possession. Builders agree for compensation 4000/month, but he claims 6 months gress period. And for that period he will not give me compensation amount.

Dear Sir, can registered will be changed if all the parties are in agreement after the death of testator? If yes what is best way? The testator have named all of his unmovable properties to only one son of two sons. Now both sons have agreed to share the properties. What is the best way to transfer one house to the the son whose name is not in the will.

I had booked office space 2 years back by paying full & final payment for fully furnished office space, means i had no payments pending till possession. now after 2 years i received offer letter of possession from builder saying "your office space is ready in pre finished state, and you are supposed to pay full& final payment and also 2 years cam charges with GST in advance but applicable from date of possession in 25 days ,after that builder will initiate pending work to fully furnish the said office space, When I refused them for 2 years , they told me to pay 1 year charges +GST IN ADVANCE otherwise they will not complete my office space and will levy interest rate on me. More over when I checked my office , even two sides wall is not constructed , no wiring points, no plaster , no false celling, only flooring done Please suggest what can I do?? Should I pay for 1year